The OTN technology is regarded as the core technology of the next-generation transport network. The OTN provides powerful Tandem Connection Monitoring (TCM) capabilities, rich Operation Administration Maintenance (OAM) capabilities, and outband Forward Error Correction (FEC) capabilities, and can schedule and manage large-capacity services flexibly.
The OTN technologies include electrical processing layer technologies and optical processing layer technologies. On the electrical processing layer, the OTN technology defines a “digital envelop” structure, which manages and monitors client signals effectively. FIG. 1 shows a structure of an OTN standard frame. An OTN frame is a 4080*4 modular structure, namely, an Optical Channel Data Unit-k (ODUk). An ODUk includes: a Frame Alignment Signal (FAS), which provides the frame alignment function; Optical Channel Transport Unit-k (OTUk) overhead, which provides the network management functions of an OTU level; ODUk overhead, which provides the maintenance and operation functions; and Optical Channel Payload Unit-k (OPUk) overhead, which provides the service adaptation function; OPUk payload area, also known as OTN frame payload area, which provides the service bearing function; and a FEC byte, which provides the functions of detecting and correcting errors. The coefficient k represents the supported bit rates and different OPUk, ODUk, and OTUk, for example, k=1 indicating a bit rate of 2.5 Gbps, k=2 indicating a bit rate of 10 Gbps, and k=3 indicating a bit rate of 40 Gbps.
The standard defines an OPUk timeslot structure that supports times division at a 2.5 G granularity. That is, a cyclical timeslot of an OPU2 (or ODU2) is divided into four timeslots, and a cyclical timeslot of an OPU3 (or ODU3) is divided into sixteen timeslots. In order to transmit low-rate services in the OTN, the standard formulates a new ODU of a 1.25 G level (namely, ODU0). The corresponding OPUk timeslot structure can support timeslot division at a 1.25 G granularity. That is, a cyclical timeslot of an OPU1 (or ODU1) is divided into two timeslots, a cyclical timeslot of an OPU2 (or ODU2) is divided into eight timeslots, a cyclical timeslot of an OPU3 (or ODU3) is divided into 32 timeslots, and a cyclical timeslot of an OPU4 (or ODU4) is divided into 80 timeslots.
In an OTN, in the communication between a network node of a 1.25 G timeslot structure and a network node of a 2.5 G timeslot structure, the network node of a 1.25 G timeslot structure uses a Generic Framing Procedure (GFP) mapping mode, encapsulates the packet service signals into an ODUk, maps the ODUk to the Optical Channel Data Tributary Unit-kt (ODTUkt), where t is greater than k, and finally maps the ODTUkt to timeslot i and timeslot i+n in a cyclical timeslot of an ODUt of a 1.25 G level (n is the number of cycles of a timeslot of an ODUt of a 2.5 G level, and the value of i falls between 1 and n) and transmits the ODTUkt to the destination node. In this way, the network node of the 2.5 G timeslot structure receives the ODUt sent by the network node of the 1.25 G timeslot structure, identifies only the indication of the ODUt included in timeslot 1 to timeslot n, and processes the ODUt.
In the process of developing the present invention, the inventor finds that: In the 2.5 G and 1.25 G timeslot structures defined in the standard, the timeslot structure of the OPU2 is different from that of the OPU3. Consequently, the transmission is restricted when the ODU0 newly defined in the 1.25 G timeslot structure is transmitted in the 2.5 G timeslot network after being carried through OPU2 or OPU3 in the 1.25 G timeslot structure, but the devices of the 2.5 G timeslot structure have been deployed in the network massively, which restricts the use range of the 1.25 G timeslot structure.